1. Technical Field
This invention relates generally to spark ignition devices for internal combustion engines, and more particularly to spark plugs having an upper insulator and to their method of construction.
2. Related Art
A spark plug is a spark ignition device that extends into the combustion chamber of an internal combustion engine and produces a spark to ignite a mixture of air and fuel within the combustion chamber. As illustrated in FIG. 1, a conventional spark plug 1 typically has an outer metal shell 2 with a ceramic insulator 3 at least partially received and captured in the shell 2. Further, an electrically conductive center electrode 4 typically extends partially through the insulator 3 to a firing tip 5 and a ground electrode 6 extends from the shell 2 to provide a spark gap 7 in conjunction with the firing tip 5. In addition, a metal terminal stud 9 is typically arranged in electrical communication with the center electrode 4. The terminal stud 9 commonly has an upper end exposed from the insulator 3, with the upper end having a specially profiled outer surface for attachment to an ignition wire.
Although the conventional spark plugs, such as discussed above, are generally effective in use, at least some of the components identified above and the associated manufacturing processes used to manufacture and assemble the components increase the overall cost to make the spark plugs. For example, the ceramic insulator 3 typically needs to be glazed on its outer surface to prevent contamination from attaching to its otherwise porous outer surface. Further, the ceramic insulator 3 typically needs to be attached and sealed with the metal shell 2 using one of two methods, i.e. hotlock or sillment seals, which requires specialized equipment. In addition, the common requirement for the outer surface of the upper end of the terminal stud 9 to be contoured requires secondary machining, thereby adding cost. Further, the metal terminal stud 9 needs to be cemented or fired within the ceramic insulator 3, again adding cost. Further yet, in order to decorate the outer surface of the ceramic insulator 3, as required by the customer, special heating equipment and processes need to be employed, adding yet further cost to the spark plug.
Accordingly, there is a need to reduce the costs associated with the manufacture and assembly of a spark plug. A spark plug manufactured and assembled in accordance with the invention has greatly reduced costs associated with its manufacture and assembly.